I've had plenty of experience trying to light convincing day interiors with a small lighting kit and have found the best thing you can do is utilise what daylight is already coming in, just in a controlled fashion. I've never had the luxury of having a 12/18K to stick outside and with the time constraints of a 48 hour competition, you want to have a simple set up that works so you can move quickly.
Windows are your biggest enemy - chances are if you can't ND them, you're not going to have the lights to bring up the levels in the room to match. If possible, just avoid having them in frame as much as possible. This issue has always plagued low budget stuff like mine.
I'm assuming you have some dialogue taking place somewhere in the room, on the couch maybe? If so, do your best to move it away from the wall and create some depth - it will be much easier to light and look much better. Utilise the curtains as makeshift flags to cut the daylight and throw some muslin on the floor to bounce the daylight up. If this doesn't work, try the ceiling. If you've got a cloudy day and the sun is going in and out, you could maybe use a 1K gelled 1/2 CTB and bounce it.
I think it will end up being a balancing act between utilising what light is already there, augmenting that, and then dialling in your white balance. I am no seasoned professional, in fact, I'm pretty new to this but I've had past experience in similar circumstances so hope some of this is helpful.